Steve, is there anything that you might suggest, the symptoms are ALWAYS: surge
The economy meter will always fluctuate with the surging, then following the surging pattern will indicate a "full fuel " condition. When this happens the economy meter stays pegged even under a trailing throttle condition. When the issue manifests itself, the car will start, if shut off without any trouble. THe exhaust will be extremely rich smelling (blue smoke).
THe issue typically happens when I am on cruise at about 120kmh (70 mph) after about an hour or more of driving.
At any other time the car performs flawlessly, with no hint of anything untoward.
Thanx in advance
A mercedes is an inanimate object and therefore must respond to logic and reason.